And Incredibly Bright

We have blotted out the night sky

In 1994, when an earthquake knocked out power in Los Angeles, many residents called 911 to express concern about a “giant, silvery cloud” in the sky. In fact, what they were looking at – perhaps for the first time – was the Milky Way. On other nights, the vast city’s millions of electric lights faded out the glowing band of stars that has connected people to the cosmos for millennia.

photo illustration Lilli Keinaenen

This alienation from the night sky is not restricted to LA residents. Nearly two-thirds of Americans now live in places where the Milky Way is no longer visible. Our cities and suburbs are so brightly lit that on any given night only 1 percent of Americans have a view of the sky unpolluted by artificial light. The range and reach of our lights is increasing every year – at a rate that experts say will cancel out every dark sky in the contiguous United States in just over a decade. Soon, all of America will have lost sight of the Milky Way. There is little global-scale data on artificial night sky brightness, but researchers at the US National Optical Astronomy Observatory in Arizona say more than one-fifth of the world’s population has already lost “naked-eye visibility” of the Milky Way.

What does this loss of natural darkness mean? In the past few decades, astronomers, medical researchers, and ecologists have been discovering the myriad, disturbing repercussions an artificially illuminated world has on us and on all life on Earth.

For astronomers, the increase of artificial night lighting – which causes light to reflect off the moisture and dust in the air and creates a glow in the sky – means the stars and planets are harder to observe. Among other things, light glare increases the difficulty of detecting potentially dangerous asteroids.

The most worrisome research on human health links nighttime light exposure to increased risk of breast cancer. The first scientist to break ground in that area was Dr. Richard Stevens, who published a report in 1987 that drew a connection between breast cancer and night-shift work. Twenty years later, in 2007, the World Health Organization, too, concluded that prolonged night-shift work could lead to cancer.

Now, new research shows that that not only working at night, but simply being in what Harvard scientist Itai Kloog calls the “modern urbanized sleeping habitat,” is a risk. Recent studies led by Kloog show a significant association between nighttime brightness and incidence of breast cancer. Most scientists believe this has something to do with the body’s ability to produce melatonin – a hormone secreted at night by the pineal gland that helps balance the reproductive, thyroid, and adrenal hormones and regulates the body’s circadian rhythm of sleeping and waking. Melatonin reduces the body’s nocturnal production of estrogen – a hormone that can stimulate growth of cancer cells. It has also been shown to slow or stop the growth of several types of cancer cells. Exposure to nighttime light, even at low levels, can seriously impede melatonin production. A 2011 Ohio State University study found that chronic exposure to dim light at night could also affect our immune system’s ability to respond to illness.

Humans aren’t the only ones impacted by light pollution. In fact, we may be far more adaptable to it than other species. “We have a bias as diurnal creatures that we don’t realize how much wildlife is active at night,” says Chad Moore, the US National Park Service’s Night Sky program manager.

While we still don’t know enough about the full ecological consequences of light pollution, scientists are finding increasing evidence that artificial light disrupts the natural activities of many species, affecting how they forage, communicate, and even reproduce.

Researchers have found, for example, that sockeye salmon fry stop swimming downstream when exposed to any light above 0.1 lux (the standard measurement for lighting) and often end up in slow-moving waters near the shore, which makes them vulnerable to predators. Some slow-flying bat species are finding it difficult to feed themselves since there are fewer hours of unalloyed darkness available to them and also because the insects that they like to eat swarm around lights at night.

In coastal areas, thousands of hatchling sea turtles that crawl out of their shells at night get disoriented by lights from beachfront homes and resorts and never make it to the safety of the sea. And every year, millions of bedazzled birds fly into our cities’ lighted high-rises and communication towers and die. A 2012 study by Travis Longcore and Catherine Rich of the Urban Wildlands Group and colleagues found that about 6.8 million birds die in North America every year by flying too close to the static red lights on communication towers and colliding with cables that hold up the tall structures. Earlier this year they published another study that breaks down those deaths by species, something that hasn’t been done before. “There aren’t just birds out there, there are many hundreds of different species of birds,” says Longcore, who along with Rich co-edited the book, Ecological Consequences of Artificial Night Lighting.

While it would be difficult to do away with night lighting, which makes much of our modern lifestyle possible, research shows as much as half of the light we project is wasted – it points up at the sky instead of illuminating the street below. Simple ways to minimize such waste and reduce light pollution include turning lights off when not in use and lighting our streets and outdoors with cutoff lights that point only downward.

Although research on the full impact of light pollution is ongoing, Moore thinks we should act now to reclaim the night. “It would be a mistake to think we need to have information on every particular species before we can act,” he says. “We know enough now that we can say anytime we spill light into the sky, we’re putting animals and wildlife at risk, and we’re probably putting ourselves at risk.”